The invention relates to a method for the continuous production of a moving mat from a stock of particles of different dimensions by means of a conveyor spreading mechanism for the manufacture of wood boards or the like by means of subsequent pressing of the mat.
By the disclosure in U.S. Pat. No. 5,012,933 a method and an apparatus for the segregation of excessively thick wood material has been made known, in which material that did not pass in the grading process was segregated by means of grading cylinders, and then was returned again to the grading process after regrinding. A grading of the material was achieved by the fact that, in a first step, a cylinder grader was used, in which the cylinders are at distance apart which increases in the direction of conveyor movement, and the material of excessively great size was discharged at the end of the first set of cylinders, while the remainder, still containing particles of the correct size and smaller, was graded in a second step to remove the fines. At the end of the cylinder train the oversize pieces were fed directly to grinders to be reground.
In a second grading process, which took place below the first grader, a separation was made again between fine material and usable material; the fines in this stage were dumped by the cylinder grader into a hopper, while the material needed for the manufacture of paper was delivered to another hopper for further processing. With a grading procedure of this kind, no mat such as can be used for the production of wood boards or the like can be built up by means of the conveyor spreading mechanism disclosed.
In German Auslegeschrift 1205274 an apparatus has been disclosed in which throw-scattered wood chips or other such spreadable particles are formed on a strand support (shaping band) into a strand which is fed continuously or in sections into a press which makes them into solid products, especially flake boards in which the particles are randomly oriented. Then, on the way from the throwing point to the strand support either one or more spring frames or one or more special throw cylinders, or one or more vortex blowers, or a combination of these or other apparatus producing the same effect, the particles coming from the throwing point have to pass by them for orientation in substantially different directions. With an apparatus of this kind it is difficult to produce a mat for the production of wood or other such boards in which wrong-size particles must not be carried into the mat. Attempts have also been made to achieve an improvement by rotary speed variations, in order to remedy such deficiencies. These attempts, however, fail.
Setting out from here, the present invention is addressed to the problem of having a well-defined throw-down plane for the particle material independently of the speed of the scatter cylinders, so that not only will no wrong particles enter the spread, but also a build-up of the particles passing through the rolls will be achieved, that will be uniform over the entire field. The definition of a space between the scatter plane and the mat plane will furthermore counteract a faulty spread.
This problem is solved by the present invention in that, during the conveyor spreading, holdout pockets are first created deliberately and continually over the entire width and length of the conveyor spreading mechanism, and from them individual spreading actions are performed for the continuous formation of the advancing mat. This brings it about that, for one thing, both the space between the starting point of the scatter and the deposition of the spread material in the mat are very well defined, and that, on the other hand, a virtually equal amount of the particle stream being spread is discharged throughout the scattering procedure.
For the embodiment of this inventive method, it is proposed that the intentional formation of the holdouts over the spread length of the conveyor spreading mechanism be made controllable. Thus it is possible, for example, in the case of a section-by-section pressing of a mat to wood flake boards, to control the density and thus the strength of the board in the lengthwise direction.
An embodiment of the inventive method consists in the fact that the intentional formation of the holdouts over the spreading width of conveyor spreading mechanism is controllable. By such control the density and thus the strength also transversely of the finished flake board can be influenced, so that in the end effect a wood material board can be produced in which predetermined strength properties can be produced both lengthwise and transversely.
In still another embodiment of the inventive method, particles unsuitable for the conveyor spreading mechanism are carried away by a conveyor separately from the conveyor spreading mechanism. By this conveyor process a definite separation of the material is achieved, which is necessary in order to produce boards of predetermined properties, and which at the same time offers the possibility for reusing the segregated material either by returning it into the spreading procedure, or in case the material is not usable, for example when glue lumps occur, of separating this material before it becomes embedded in the board, as it is claimed in the inventive characteristic of claim 4.
In a preferred embodiment the rejected particles are fed to a re-grinding apparatus, at the end of which usable particles are recycled, and unusable particles are separated out. In this way a reduction of waste is achieved, and the recycling of such material is made possible, for example in the use of wood which has a very slight thickness, yet in other dimensions has a considerable surface area.
In still another embodiment of the method, depending on the particles to be spread, and depending on how the advancing mat is formed by conveyor spreading, a predetermined separation of the particles is accomplished. Merely by means of the predetermined separation of the particles based on the particle stream and the throughput of the conveyor spreading mechanism, it is possible to produce predetermined cross-sectional patterns through the thickness of the mat.
Setting out from an apparatus with a bunker for spreading particles which discharges to an adjoining spreading station whose width corresponds to the width of the mat and has a series of revolving spreading rolls disposed in the spreading station and provided with a texture, plus a support continuously moving under the spreading station for receiving a spread flake mat that is to be pressed for the production of wood or similar boards, it is proposed that the circumferential surfaces of each spreading roll have first equally long, channel-like pockets in a plurality of rows alternating in the circumferential direction, and offset therefrom a plurality of rows with second, equally long, channel-like pockets, that each row of the channel-like pockets be separated from the next row by lands on the circumferential surface, and that the first and second equally long, channel-like pockets in the axial direction of each spreading roll be separated by lands over the entire length of the circumferential surface of the spreading roll, so that each channel-like pocket constitutes a separate indentation in the circumferential surface. With this apparatus according to the invention, predetermined amounts of the particles issuing from the bunkers can be formed, and at the same time cause, by the rotation of the series of spreading rolls, a transport by which also the other, distinct indentations in the spreading rolls are filled simultaneously, so that, upon the continued rotation of the spreading rolls a conveyor spreading mechanism results, in which substantially equal amounts of spread material can be let out of the rotating spreading rolls at the same time and be deposited on the continuously advancing support.
As an embodiment of the apparatus of the invention each spreading roll bears second equally long channel-like pockets at an angle to its axis, that offset therefrom several rows are provided with second, equally long channel-like pockets whose channel axes are at an angle to the slanted channel axes of the first equally long channel-like pockets. By the arrangement of equally long channel-like pockets at an angle to one another, but which do not run through one another, it is brought about according to the invention that, especially in the case of rotating spreading rolls that are directly in contact with one another at their surfaces, any pinching or jamming of chip material before it reaches the channel-like recesses is prevented, and also that the transport through the entire array of revolving spreading rolls disposed in tandem operates faultlessly. Thus a still further improved holdover in the channel-like pockets is achieved, which then, as the spreading rolls continue to rotate, permits a precise distribution from these holdover pits onto the support running along thereunder.
In a preferred embodiment of the invention the angle between the first and second equally long channel-like pockets is greater than 0 degrees and less than 180 degrees. Thus, in the case of a plurality of tandem rotating spreading rolls configured according to the invention, a row of pocket-like pits which are closed off from the particles dropping from above, i.e., from the bunker, in the area of contact of the circumferential surfaces, by lands running in the direction of the longitudinal axis of the spreading rolls and in the direction of the circumference of the spreading rolls. The slanting of the spreading pits at the angle specified by the invention, facilitates the filling of the pits.
In yet another embodiment of the apparatus according to the invention, the channel-like pockets have semicircular curves at their extremities on the circumference of the roll. The semicircular curve facilitates the intertwining of particles during the filling and emptying of the channel-like pockets.
In yet another embodiment of the apparatus according to the invention, the channel-like pockets are rounded off from the circumference of the roll to the bottom of the channel, perpendicular to the direction of the channel axis. This configuration of the channel also promotes both the filling and the emptying of the channel-like pockets; it serves also to facilitate a squeezing of the particles being fed through the cylinders against the adjacent rolls of the conveyor spreading apparatus which produces the conveyor spreading mechanism.
In another embodiment of the channel-like pockets according to the invention the channel-like pockets have rounded cross sections. This embodiment of the invention contributes to keeping the channel-like pockets clean.
In a preferred embodiment, the apparatus of the invention is characterized in that each spreading roll consists of two cylinder sleeves arranged in tandem along the axis and having channel-like pockets of equal length, and in that the lands between them are continuous over the entire length of the spreading roll. By making the spreading rolls from sleeves, in the first place a considerable saving of weight is achieved in comparison with solid rolls based the same outside diameter, and in the production of the surface of the roll considerable savings are achieved by the fact that any desired spreading roll lengths can be made up of individual roll sleeve units in the manner of a modular system, without the need to invest in more tooling for the manufacture of exceedingly long and slender spreading rolls. Also, dividing the total length of the spreading rolls into sleeve units of different lengths counteracts the flexure of a spreading roll made up of sleeves.
In further development of the apparatus visible circumferential abutting edges occurring between at least two tandem spreading roll sleeves are not in alignment with one another. This brings it about that no harmful effects will be propagated from the abutting edges through the entire series of the rotating spreading rolls.
In a preferred embodiment visible abutting edges occurring between the sleeves run spirally over the circumferential surface of the single spreading roll. This embodiment also serves to prevent any sources of error that might be created by the abutting edges.
In a preferred embodiment, there are provided of two sleeves an abutting edge between the sleeves is disposed away from the center between the two sleeve surfaces. This constitutes an especially preferred embodiment of the invention for the prevention of the sagging of spreading rolls in sleeve form.
In regard to the configuration of the channel-like pockets, the distance (depth) between the spreading roll's circumferential surface and the bottom of the channel-like pockets differs from roll to roll. This makes it possible to hold out additional material in the channel-like pockets of the downstream and upstream pairs of spreading rolls through the transport section, i.e., during the conveyor spreading action. Thus on the one hand the throughput in such conveyor spreading mechanisms is increased while the quality of the spreading remains the same, and on the other hand any influence on the spreading quality is avoided.
In a preferred embodiment of the apparatus the distance (depth) between the circumferential surface of the spreading roll and the bottom of the channel-like pockets differs over the length of the length of the individual spreading roll. By this arr transversely of the direction of the advance of the mat in formation, which is then processed to wood or other such boards, serves to produce a greater density in the marginal area of these wood material boards, which can be of advantage in the case of a spline-and-groove design of such boards.
In a preferred embodiment of the apparatus it is proposed that the uninterrupted lands on the surface of the spreading roll terminate in cutting edges. Thus, the particle throughput can be increased considerably, no pinching of the particles occurs, and furthermore a well-defined discharge from the pockets takes place uniformly.
In another embodiment of the present invention, the rolling process, the pressure-casting or injection molding process is used in the preparation of the surfaces of the spreading rolls according to the method for the continuous production of a mat according to the present invention.
In a preferred embodiment, spreading rolls made according to the invention are characterized in that their circumferential surface is then subjected to a machining procedure. The machining of the circumferential surface makes it possible for the first time for spreading rolls designed for a conveyor spreading system to provide for the positive and smooth control of the particle stream needed for the spreading, even in the case of direct contact of their circumferential surface.
Therefore, it is possible for the first time, by means of the sets of spreading rolls with a smooth but indented surface to form continuously a well-defined mat from a stream consisting of particles of different dimensions, wherein, depending upon the direction of movement of the support for receiving the mat and/or the arrangement of the spreading rolls according to the invention disposed in tandem and performing the conveyor spreading mechanism, to produce a mat on the support, the cross section of which is continuously formed beginning from a topmost layer with fine particles, then a layer with coarser or coarse particles, and thereafter, again with fine particles, the other outside layer of the mat.
It can, of course, be understood that a mat thus made can be used by itself, or parts of it, for the facing of other mats in order to produce therefrom wood or similar boards by pressing.
The invention will be further explained in the following description of embodiments thereof.